FIGS. 1 and 2 are schematic sectional views of a conventional high-frequency heating apparatus equipped with a temperature probe having a jack on the oven top plate.
A motor 2 is disposed at the bottom of an oven chamber 1. A turntable 5 supported by rollers 4 is rotatably carried by the motor 2 through a rotary shaft 3. Food 6 placed on the turntable is heated by microwaves. With the temperature detector means 8 of a temperature probe 7 inserted into the food 6, temperature data are transferred through a cable 9 and a plug 10. A jack 11 in a device for rotatably supporting the temperature probe 7 is secured, through a choke cover 12 for preventing leakage of electric waves, to an oven top plate 1A at or adjacent its center axis corresponding to the center of the turntable 5. The plug 10 of the temperature probe 7 is held by a resilient metallic plate 13. Electric signals are adapted to be taken out from an electric output terminal 14A and an electric output terminal 14B pressed by a sleeve 15. These terminals 14A and 14B are insulated from each other by an insulator 16. A resin pipe 17 surrounding the jack 11 assures slide and rotation of the jack 11.
Vapor produced by the food 6 when it is heated, is adapted to be discharged to the outside after having passed through exhaust ports 1B in the oven top plate 1A and a louver means 18A of a body 18.
The plug 10 of the temperature probe 7 is secured to the jack 11 which is rotatable. In order to assure rotation of the jack 11, the pipe 17 is required.
According to such a construction, electric waves may leak from the inside of the oven chamber 1 to the outside. In order to prevent such leakage, a large choke cover 12 is indispensable, so that the apparatus is complicated in construction and is relatively large.
FIG. 2 illustrates the high-frequency heating apparatus of FIG. 1 with the temperature probe 7 removed from the temperature probe mounting unit, so that the apparatus is used as a normal microwave oven.
When the apparatus is used in such way, the temperature probe 7 and the jack or device 11 for rotatably supporting the temperature probe 7 are exposed directly to vapor, oil or stock produced from heated food in the heating chamber. In particular, the inside of the probe rotatably supporting device or jack 11 which is hermetically sealed, is always filled with vapor. The resilient metallic plate 13, the sleeve 15 and the insulator 16 therefore get rusty and dirty, thus provoking an increase in contact resistance and decrease in insulation resistance. When the temperature probe 7 is inserted into the jack 11 to be connected thereto as necessary, such increase in contact resistance and drop in insulation resistance disable accurate transmission of electric signals to a temperature control circuit disposed outside of the oven. In the worst case, no electrical conduction is made.
In the inside of the probe rotatably supporting device or jack 11 which is filled with vapor, vapor is converted into waterdrops due to dew condensation. The water-drops are therefore attached to the resilient metallic plate 13, the sleeve 15 and the insulator 16. The resilient metallic plate 13 is connected to the sleeve 15 through such waterdrops. Resistance is therefore produced on the electric output terminals 14A and 14B. The control circuit outside of the oven is actuated as the temperature probe 7 would be inserted in the jack 11 to be connected thereto, thereby to erroneously stop normal microwave oven operation. Until such communication through waterdrops is removed, normal microwave oven operation cannot be obtained.
Moreover, the hermetical sealing construction of the probe rotatably supporting device or jack 11 delays evaporation of such waterdrops. It disadvantageously takes much time before normal operation is obtained.